In recent years, batteries with reduced size, reduced weight, and increased energy density have been required as drive power sources for various electric apparatuses such as personal computers, particularly along with their tendency toward cordless and portable configurations. In particular, non-aqueous electrolyte secondary batteries such as lithium ion batteries have high energy density, and are expected as leading products that meet such requirements.
Some non-aqueous electrolyte secondary batteries have a rectangular structure with an electrode member in which a positive electrode and a negative electrode are laminated via a separator, and others have a cylindrical structure with an electrode member formed by winding a laminated member including a positive electrode and a negative electrode laminated via a separator. The electrode member of either structure is housed in a battery case or a battery casing together with a non-aqueous electrolyte. It should be noted, however, that the battery case may have a rectangular outer shape even if a wound electrode member is used as the electrode member.
In the non-aqueous electrolyte secondary batteries, further, a current is drawn from the electrode member via a positive current collecting member and a negative current collecting member connected to the positive electrode and the negative electrode, respectively. That is, the current collecting members are fixed at an end portion of the electrode member, and a positive terminal and a negative terminal connected to the positive current collecting member and the negative current collecting member, respectively, for electrical conduction are projected out of the battery case through terminal leading holes (terminal through holes) formed in a lid of the battery case. In an example of a seal structure for the terminal leading holes, a seal member (for example, a gasket) is provided between an inner wall surface around a portion of the lid formed with the terminal leading holes and terminal body portions of the electrode terminals having threaded terminal portions when the electrode terminals are inserted through the terminal leading holes of the battery case from the inner side of the battery case, and a nut is fastened via a washer and the gasket onto a threaded portion of the threaded terminal portions of the electrode terminals projecting out of the battery case to pull up the electrode terminals out of the battery case and compress the seal member between the inner wall surface of the lid and the terminal body portions of the electrode terminals (see Patent Documents 1, 2, and 3, for example).